Electrophotographic copier

ABSTRACT

An electrophotographic copier is disclosed having a rotatable photoconductive drum, means to apply a uniform electrostatic charge pattern thereto, means to expose the uniform charge pattern to a light image of an original, and unique development, transfer and fusing systems. The development system is a high efficiency development system which increases the radial velocity components of developer over that normally associated with cascade development. The transfer and fusing system includes an elastomeric transfer belt, preferably having a low heat capacity and being formed from a silicone elastomer, operating in combination with a radiant fuser and a paper transport system which provides increased thermal efficiency. These systems interrelate to provide a copier which is compact, high speed, produces excellent quality copies and consumes lower amounts of power than are normally associated with high speed copiers.

United States Patent 1191 1111 3,923,392 Buchan et al. 1 1 Dec. 2, 1975 [541 ELECTROPHOTOGRAPHIC COPIER 3,685,896 8/1972 Kaupp 355/3 R [75] Inventors: William R. Buchan, Lincoln; James I E. Genthe, Chelmsford; Edward F. Pr'mary Exammer j9hn Hora Mayer, Acton, an of Mass; Robert Attorney, Agent, or Firm-Homer 0. Blair; Robert L. A Moore, Amherst, NH Nathans, David E. Brook [73] Assignee: ltek Corporation, Lexington, Mass. [57] ABSTRACT Filed: Jan. 2, 1974 An electrophotographic copier is disclosed having a [21] Appl No: 429,617 rotatable photoconductive drum, means to apply a uniform electrostanc charge pattern thereto, means to expose the uniform charge pattern to a light image of [52] U.S. Cl 355/3 R an original, and unique development transfer and fus- Int. (:l. systems The development ystem is a effi- Field Of Search 5 3 8/ 3 ciency development system which increases the radial 8/ velocity components of developer over that normally associated with cascade development. The transfer [56] f r n s C t and fusing system includes an elastomeric transfer UNITED STATES PATENTS belt, preferably having a low heat capacity and being 2,927,554 3/1960 OldeIlbOOn 117/175 x fOFITIed T a smFcme elastome" Operating in COmbi' 2,990,278 6/1961 Carlson 118/637 X "anon Wlth a radlam fuser and a P p transport y 3 013,878 12/196] 136556116, 117/175 X tem which provides increased thermal efficiency. 3,336,905 8/1967 Lehmanni. 118/637 UX These systems interrelate to provide a copier which is 3,416,494 /1 8 H ds n 117/175 X compact, high speed, produces excellent quality cop- Byrne R ies and onsumes lower amounts of power than are 3,620,191 ll/l97l LyleS 8/637 normally associated with g Speed pi 3,638,6ll 2/l972 We1leret al.. 117/175 X 3,648,658 3/1972 Weiler 118/637 9 Claims, 1 Drawing Figure IMAGING 5771/70/1/ 40 MODIFIED CASCADE DE VE LOPE Fr 50 BIAS SOURCE CORONA "i -1 STAT/O/VJO PHOTOCONDUCT/ l/E DRUM [0 RAD/ANT HEA r07 TRANSFER AND FUS/ll/G SHIT/0N 60 BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to an electrophotographic copier.

2. Description of the Prior Art Many electrophotographic copiers are designed to carry out an electrostatic process wherein a conductive backing having a photoconductive insulating layer thereon is electrostatically imaged by first uniformly charging its surface and subsequently exposing the charged surface to a pattern of activating electromagnetic radiation such as light. The radiation pattern selectively dissipates electrostatic charges in illuminated areas on the photoconductive surface to produce a latent electrostatic image in non-illuminated areas. This latent electrostatic image can be developed to form a visible image by depositing developer materials thereon by a variety of development techniques, the most common of which is cascade development in which solid developer is cascaded across the latent image. Solid developer materials are customarily two component systerns containing finely divided pigmented particles commonly called toner, and relatively coarser, larger beads commonly called carrier beads. The developed toner image is transferred to a final substrate medium, such as plain paper, by electrostatic transfer, pressure contact, or otherwise. Once transferred, the toner image is fused or fixed to the final substrate medium by heat, solvent vapor, a fixative coating, etc.

It is desirable to have copiers as described above which produce copies rapidly, but high speed electrophotographic copiers heretofore available have had a number of features which it is desirable to improve. Usually, for example, high speed copiers are large, bulky machines which consume large amounts of power. Additionally, copy quality often suffers on such machines, particularly in features such as background. It is desirable to produce copies with minimum background levels, i.e., developer in non-image areas, but this has not been possible with most high speed machines.

SUMMARY OF THE INVENTION The invention comprises an electrophotographic copier comprising a number of unique features which interrelate so that the copier is compact, produces high quality copies rapidly, and requires smaller amounts of power than is customary with high speed copiers. A photoconductive member, which is perferably a relatively small diameter drum, is used to produce the electrostatic image. Development is achieved with a highly efficient development apparatus, preferably in a modified cascade development apparatus which interferes with the normal flow of developer, particularly in such a way as to increase the radial velocity of toner particles over that present in conventional cascade developers. The developed toner image is transferred from the photoconductive drum by an intermediate elastomeric belt. Excellent thermal efficiency is achieved by designing the belt to have a low heat capacity, by using a radiant heater, and by providing a paper transport system which maintains contact between the belt and paper for relatively long periods. It is believed that the combination ofa high efficiency development apparatus, particularly one imparting substantial radial velocity components to the developer, together with an elastomeric transfer belt, particularly one made of silicone rubbers, fluoroelastomers, or their equivalents, result in copies having exceptionally low background.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates schematically an electrophotographic copying apparatus of this invention employing a modified cascade development system with a thermally efficient transfer, fusing and paper handling systern.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring now to FIG. 1 in more detail, a photoconductive drum 10 is shown which typically consists of a conductive metal substrate 11, such as aluminum, coated on its outer surface with a layer of photoconductive insulating layer 12, typically vitreous selenium. Drum 10 rotates at its axis and is shown rotating in a counterclockwise or downhill" direction.

A cleaning station 20 is provided to remove residual toner from the photoconductive drum 10 prior to the start of each imaging sequence. Cleaning station 20 includes a fur cleaning brush 21 mounted on slidable element 22 so that the brush can be disengaged.

A uniform electrostatic charge is formed on the surface of drum 10 by means of corona charging station 30. This station includes corona element 31 which is electrically connected to a power source such as battery 32 and to ground.

Uniformly charged drum 10 then passes imaging station 40. Light sources 41 illuminate original 42 which is imaged through imaging lens 43 and slit 44 to form an electrostatic latent image of the original on the surface of photoconductive drum 10. Scanning optics can also be used, but fixed optics are preferred to maintain compactness.

The copier illustrated in FIG. 1 is a compact but high speed copier. Its size is kept relatively small by using a small diameter photoconductive drum. The drum might be, for example, nominally five inches in diameter, which is required to handle conventional originals such as 8% X 11 inch typed pages. Because the drum is small, it must be rotated at relatively high speeds to produce copies rapidly; typically this means that the drum must move at a speed of about 10 inches/second or more. Because of the shorter development zone and higher drum speed, highly efficient development systems are required. Cascade developers can be modified to provide such highly efficient development apparatuses, and one such modified cascade developer is illustrated in FIG. 1.

Cascade development apparatus 50 includes a housing 51 including within it a bucket elevator system formed by an endless belt 52 having buckets 53 thereon. Electrostatic developer is lifted from a reservoir section 54 in buckets 53 to a point at the upper portion of drum l0 and then cascaded over the drum surface by means of feed guide 55. As developer cascades over drum l0, toner particles separate from the carrier beads and deposit on the drum surface in accordance with the latent electrostatic image thereon, thus forming a visible toner image. Spent developer is guided back into reservoir 54 by guide 56. The biased development electrode 57 has a roughened surface 58 which can be formed by knurling its surface or otherwise forming protuberances thereon. This roughened surface interferes with the normal flow of developer and is particularly effective at increasing the radial velocity of toner through the development zone to effect increased developer efficiency..For a more detailed description of this type of modified cascade development apparatus, see our copending application in the names of William R. Buchan and James E. Genthe, Attorneys Docket No. l-485, filed concurrently herewith.*

*This copending patent application is incorporated by reference herein.

Other high speed high efficiency development apparatuses could be used; the important parameter being development efficiency. Included, are such development systems as magnetic brushes, fur brushes, fluidized bed developers, cascade development apparatus modified by moving belts, uphill cascade developers. These systems are well known to those skilled in the art.

Transfer and fusing station 60 is designed to keep the copier compact, provide outstanding thermal efficiency thereby lowering the overall power requirements for the copier and to produce clean, low background copies. An intermediate transfer belt 61 is trained to pass in an endless loop around rollers 62, 63, 64, 65, 66 and 67. Belt 61 is driven by suitable means such as motor 68 which is connected to and drives roller 67 in a clockwise direction. Roller 62 can be adjusted by tensioning spring 69 to take up any slack created in intermediate transfer belt 61 caused by any dimensional changes due to variations in temperature or otherwise. Roller 62 is also preferably constructed of hard rubber which is electrically leaky so that any background electric charges built up on belt 61, such as triboelectric charges built up between any of the rollers and the belt, will dissipate naturally before the belt contacts photoconductive drum 10.

Transfer is accomplished at T i.e., the point at which belt 61 contacts photoconductive drum 10. Transfer is controlled by transfer roller 70 which is positioned at the back side of transfer belt 61 so that it can be moved in and out by adjusting tensioning spring 71.

Paper 72 is fed from paper roll 73 and brought into contact with the toner image on belt 61 by guide rollers 74 and 75 acting in cooperation with belt rollers 65 and 66. The contact zone between belt and paper is deliberately designed to be elongated so that paper 72 absorbs heat from belt 61 and carries it out of the copier. The exact length of this elongated zone will depend on many factors such as the speed at which the paper and belt are moving, but in general should be sufficient to leave the belt and paper in contact for at least 0.5 seconds.

Heat is supplied in a selective manner to the toner image on belt 61 by radiant heater 80. Radiant heater 80 consists of two radiant heating lamps 81 surrounded by a heat shield 82 which is properly insulated and slidable shield 83. Slidable shield 83 can be positioned directly under lamps 81 when the copier is in a standby state so that lower amounts of power can be supplied to lamps 81 while still maintaining the chamber at a high temperature. When copying is initiated, slidable shield 83 is moved to the left in which position lamps 81 radiating heat to belt 61 so that copying can begin. Because the chamber is maintained at an elevated temperature in the standby mode, copying can begin immediately even though the lamps have not risen to full power.

Transfer and fusing station 60 is designed to provide the type of thermal efficiency required in high speed copying systems if large amounts of power are to be avoided. Intermediate transfer belt 61, for example, is fabricated from appropriate materials in relatively thin layers to provide the belt with a low heat capacity, i.e., below about 3.1 X l0 cal./cm. /C. Additionally, heat absorption in the substrate for belt 61 can be eliminated or substantially diminished by coating it with a thin reflecting layer such as aluminum. Thetransfer surface of belt 61 can be formed from many materials, the preferred materials being silicone rubbers such as General Electric RTV 615 or Dow Coming 3140 and certain fluoroelastomers. A typical belt is comprised of a polyimide substrate of 0.55 mils coated with a reflecting layer of aluminum about 300 angstroms thick and a silicone rubber transfer surface 0.1-10 mils thick. Suitable transfer belts are described in detail in our copending application Ser. No. 403,696, filed Oct. 4, 1973, the teachings of which are hereby incorporated by reference.

Transparent transfer belts can also be used to increase thermal efficiency and a suitable transparent belt is disclosed by Carlson in U.S. Pat. No. 3,374,769.

The transfer belts should also have certain surface properties so that efficient transfer of toner is possible. The surface should be smooth, have good release properties (e.g., surface free energy below 40 dynes per centimeter), and have the proper hardness (e.g., about 3 to durometers on the Shore A scale).

Fusing system also contributes to the overall thermal efficiency of the copier. As mentioned above, a radiant fusing system is chosen because radiant heat tends to selectively heat toner on the surface of belt 61.

Additionally, slidable shield 83 allows the machine to consume lower power in a standby condition, but to produce copies immediately upon startup since shield 83 stores heat within the lamp chamber in its closed position.

Thermal efficiency is also built into the paper transport system since paper exiting from the machine acts as a heat sink. Because of this, the paper and belt are kept in contact for significant amounts of time as mentioned above. Besides carrying unwanted heat out of the machine, this elongated contact also removes any heat present in the belt which eliminates heat transfer back to photoconductive drum 10 at T Other transfer and fusing systems or modifications can be used providing they result in the type of thermal efficiency described herein. For example, transfer at T is illustrated as being achieved by pressure contact between belt 61 and drum 10. Nevertheless, electrostatic transfer can be used, and in some cases might even be an advantage since a thin air space would then be provided to insulate photoconductive drum 10 from any back transfer of heat. Additionally, other fusing systerns such as microwave fusing systems might also be provided which would result in the selective transfer of heat to the toner and the other general heat efficiencies mentioned. The final support medium is illustrated as being paper, which is most commonly used, but other final substrate mediums could be used in place of the paper.

The copier described herein can be operated in an image preservation mode. That is, multiple copies can be made from one exposure. This mode of operation does further the goals of providing a high speed but compact copier.

What is claimed is:

1. An electrophotographic copier comprising, in combination:

a. a rotatable drum having a photoconductive, insulating surface thereon;

b. means to apply a uniform electrostatic charge pattern to the surface of said drum;

0. means to expose said uniform electrostatic charge pattern to a light image of an original thereby forming a latent electrostatic image of the original on the surface of said drum;

d. cascade developer means for cascading electroscopic developer over said latent electrostatic image, said cascade developer means including a member closely positioned to the surface of said photoconductive drum and defining a narrow development zone therebetween, said member having a roughened surface facing the surface of said photoconductive drum, whereby the density of developer and radial velocity of developer are both increased as developer cascades through said narrow development zone;

e. an elastomeric intermediate transfer belt positioned to remove the developed toner image from the surface of said drum;

f. radiant heating means for heating the toner image on said electrostatic transfer belt; and,

g. paper transport means for bringing paper into contact with the heated toner image on said transfer belt whereby said image is transferred and fused to said paper, said paper transport means also including means for providing for an elongated zone of contact between said transfer belt and said paper after transfer of the toner image to the paper.

2. A copier of claim 1 wherein said means for applying electroscopic developer comprises a modified cascade development system which interferes with the cascade flow of developer in the development zone to increase the radial velocity components of said developer particles.

3. A copier of claim 2 wherein said modified cascade development system includes a development electrode closely spaced from the surface of said drum, said electrode having a roughened surface facing said drum.

4. A copier of claim 1 wherein said member closely positioned to the surface of said photoconductive drum is a development electrode.

5. A copier of claim 4 wherein said intermediate transfer belt comprises a relatively thin, silicone, elastomeric transfer belt having a heat capacity of below about 3.1 X 10 cal./cm. /C.

6. In a xerographic copier, the improvement comprising:

a. a rotatable drum bearing an electrostatic image to be developed by the application of particulate development material thereto;

b. an elongated development plate positioned adjacent said drum for providing an air gap containing said particulate developer, said development plate having means associated therewith for partially converting the tangential momentum of said particulate development material passing through said air gap into radial momentum;

c. an intermediate elastomeric transfer belt for receiving the resulting toner image produced upon said drum; and,

(1. means for transferring the developed image from said intermediate transfer belt to one or more receptor sheets.

7. The combination as set forth in claim 6 wherein said development plate has protuberances thereon for effecting said momentum conversion.

8. The combination as set forth in claim 6 wherein said elastomeric transfer belt is made of material selected from the group consisting of silicone rubber and fluoroelastomers.

9. The combination as set forth in claim 7 wherein said elastomeric transfer belt is made of material selected from the group consisting of silicone rubber and fluoroelastomers. 

1. An electrophotographic copier comprising, in combination: a. a rotatable drum having a photoconductive, insulating surface thereon; b. means to apply a uniform electrostatic charge pattern to the surface of said drum; c. means to expose said uniform electrostatic charge pattern to a light image of an original thereby forming a latent electrostatic image of the original on the surface of said drum; d. cascade developer means for cascading electroscopic developer over said Latent electrostatic image, said cascade developer means including a member closely positioned to the surface of said photoconductive drum and defining a narrow development zone therebetween, said member having a roughened surface facing the surface of said photoconductive drum, whereby the density of developer and radial velocity of developer are both increased as developer cascades through said narrow development zone; e. an elastomeric intermediate transfer belt positioned to remove the developed toner image from the surface of said drum; f. radiant heating means for heating the toner image on said electrostatic transfer belt; and, g. paper transport means for bringing paper into contact with the heated toner image on said transfer belt whereby said image is transferred and fused to said paper, said paper transport means also including means for providing for an elongated zone of contact between said transfer belt and said paper after transfer of the toner image to the paper.
 2. A copier of claim 1 wherein said means for applying electroscopic developer comprises a modified cascade development system which interferes with the cascade flow of developer in the development zone to increase the radial velocity components of said developer particles.
 3. A copier of claim 2 wherein said modified cascade development system includes a development electrode closely spaced from the surface of said drum, said electrode having a roughened surface facing said drum.
 4. A copier of claim 1 wherein said member closely positioned to the surface of said photoconductive drum is a development electrode.
 5. A copier of claim 4 wherein said intermediate transfer belt comprises a relatively thin, silicone, elastomeric transfer belt having a heat capacity of below about 3.1 X 10 3 cal./cm.2/*C.
 6. In a xerographic copier, the improvement comprising: a. a rotatable drum bearing an electrostatic image to be developed by the application of particulate development material thereto; b. an elongated development plate positioned adjacent said drum for providing an air gap containing said particulate developer, said development plate having means associated therewith for partially converting the tangential momentum of said particulate development material passing through said air gap into radial momentum; c. an intermediate elastomeric transfer belt for receiving the resulting toner image produced upon said drum; and, d. means for transferring the developed image from said intermediate transfer belt to one or more receptor sheets.
 7. The combination as set forth in claim 6 wherein said development plate has protuberances thereon for effecting said momentum conversion.
 8. The combination as set forth in claim 6 wherein said elastomeric transfer belt is made of material selected from the group consisting of silicone rubber and fluoroelastomers.
 9. The combination as set forth in claim 7 wherein said elastomeric transfer belt is made of material selected from the group consisting of silicone rubber and fluoroelastomers. 